Fat Body p53 Regulates Systemic Insulin Signaling and Autophagy under Nutrient Stress via Drosophila Upd2 Repression

The tumor suppressor p53 regulates multiple metabolic pathways at the cellular level. However, its role in the context of a whole animal response to metabolic stress is poorly understood. Using Drosophila, we show that AMP-activated protein kinase (AMPK)-dependent Dmp53 activation is critical for sensing nutrient stress, maintaining metabolic homeostasis, and extending organismal survival. Under both nutrient deprivation and high-sugar diet, Dmp53 activation in the fat body represses expression of the Drosophila Leptin analog, Unpaired-2 (Upd2), which remotely controls Dilp2 secretion in insulin-producing cells. In starved Dmp53-depleted animals, elevated Upd2 expression in adipose cells and activation of Upd2 receptor Domeless in the brain result in sustained Dilp2 circulating levels and impaired autophagy induction at a systemic level, thereby reducing nutrient stress survival. These findings demonstrate an essential role for the AMPK-Dmp53 axis in nutrient stress responses and expand the concept that adipose tissue acts as a sensing organ that orchestrates systemic adaptation to nutrient status.Fil: Ingaramo, María Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Sánchez, Juan Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Perrimon, Norbert. Harvard Medical School; Estados UnidosFil: Dekanty, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentin

A dp53-Dependent Mechanism Involved in Coordinating Tissue Growth in Drosophila

A study in the Drosophila wing suggests a crucial role of p53 in the coordination of growth between adjacent cell populations to maintain organ proportions and shape. Coordination of growth between and within organs contributes to the generation of well-proportioned organs and functionally integrated adults. The mechanisms that help to coordinate the growth between different organs start to be unravelled. However, whether an organ is able to respond in a coordinated manner to local variations in growth caused by developmental or environmental stress and the nature of the underlying molecular mechanisms that contribute to generating well-proportioned adult organs under these circumstances remain largely unknown. By reducing the growth rates of defined territories in the developing wing primordium of Drosophila, we present evidence that the tissue responds as a whole and the adjacent cell populations decrease their growth and proliferation rates. This non-autonomous response occurs independently of where growth is affected, and it is functional all throughout development and contributes to generate well-proportioned adult structures. Strikingly, we underscore a central role of Drosophila p53 (dp53) and the apoptotic machinery in these processes. While activation of dp53 in the growth-depleted territory mediates the non-autonomous regulation of growth and proliferation rates, effector caspases have a unique role, downstream of dp53, in reducing proliferation rates in adjacent cell populations. These new findings indicate the existence of a stress response mechanism involved in the coordination of tissue growth between adjacent cell populations and that tissue size and cell cycle proliferation can be uncoupled and are independently and non-autonomously regulated by dp53. The coordination of growth within and between organs contributes to the generation of functionally integrated structures and well-proportioned animals and plants. Though these issues have fascinated biologists for centuries, the responsible molecular mechanisms remain largely uncharacterized. In this work, we have used the Drosophila wing primordium to show that adjacent cell populations grow and proliferate in a coordinated manner. By reducing growth rates in specific territories within the developing wing, we showed that the tissue responds as a whole and that in adjacent cell populations the growth and cell cycle rates are concomitantly reduced, thus maintaining tissue proportions and normal wing shape. Interestingly, we show that the Drosophila tumour suppressor protein dp53 and apoptotic machinery play a key role in coordinating this tissue-wide response. Both growth and proliferation rates are regulated in a coordinated and non-autonomous manner by the activity of dp53, whilst the apoptotic pathway has a specific and non-autonomous role in regulating cell proliferation rates. Our studies describe a novel mechanism for regulating tissue growth in developing organs that may ultimately be relevant for other processes involving coordination of growth, such as tissue renewal, regeneration, and cancer

Oxygen Sensing in Drosophila: Multiple Isoforms of the Prolyl Hydroxylase Fatiga Have Different Capacity to Regulate HIFα/Sima

Background: The Hypoxia Inducible Factor (HIF) mediates cellular adaptations to low oxygen. Prolyl-4-hydroxylases are oxygen sensors that hydroxylate the HIF alpha-subunit, promoting its proteasomal degradation in normoxia. Three HIFprolyl hydroxylases, encoded by independent genes, PHD1, PHD2, and PHD3, occur in mammals. PHD2, the longest PHD isoform includes a MYND domain, whose biochemical function is unclear. PHD2 and PHD3 genes are induced in hypoxia to shut down HIF dependent transcription upon reoxygenation, while expression of PHD1 is oxygen-independent. The physiologic significance of the diversity of the PHD oxygen sensors is intriguing. Methodology and Principal Findings: We have analyzed the Drosophila PHD locus, fatiga, which encodes 3 isoforms, FgaA, FgaB and FgaC that are originated through a combination of alternative initiation of transcription and alternative splicing. FgaA includes a MYND domain and is homologous to PHD2, while FgaB and FgaC are shorter isoforms most similar to PHD3. Through a combination of genetic experiments in vivo and molecular analyses in cell culture, we show that fgaB but not fgaA is induced in hypoxia, in a Sima-dependent manner, through a HIF-Responsive Element localized in the first intron of fgaA. The regulatory capacity of FgaB is stronger than that of FgaA, as complete reversion of fga loss-of-function phenotypes is observed upon transgenic expression of the former, and only partial rescue occurs after expression of the latter. Conclusions and Significance: Diversity of PHD isoforms is a conserved feature in evolution. As in mammals, there are hypoxia-inducible and non-inducible Drosophila PHDs, and a fly isoform including a MYND domain co-exists with isoforms lacking this domain. Our results suggest that the isoform devoid of a MYND domain has stronger regulatory capacity than that including this domain.Fil:Acevedo, J.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Centanin, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Dekanty, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Wappner, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Drosophila Genome-Wide RNAi Screen Identifies Multiple Regulators of HIF–Dependent Transcription in Hypoxia

Hypoxia-inducible factors (HIFs) are a family of evolutionary conserved alpha-beta heterodimeric transcription factors that induce a wide range of genes in response to low oxygen tension. Molecular mechanisms that mediate oxygen-dependent HIF regulation operate at the level of the alpha subunit, controlling protein stability, subcellular localization, and transcriptional coactivator recruitment. We have conducted an unbiased genome-wide RNA interference (RNAi) screen in Drosophila cells aimed to the identification of genes required for HIF activity. After 3 rounds of selection, 30 genes emerged as critical HIF regulators in hypoxia, most of which had not been previously associated with HIF biology. The list of genes includes components of chromatin remodeling complexes, transcription elongation factors, and translational regulators. One remarkable hit was the argonaute 1 (ago1) gene, a central element of the microRNA (miRNA) translational silencing machinery. Further studies confirmed the physiological role of the miRNA machinery in HIF–dependent transcription. This study reveals the occurrence of novel mechanisms of HIF regulation, which might contribute to developing novel strategies for therapeutic intervention of HIF–related pathologies, including heart attack, cancer, and stroke

A dp53-Dependent Mechanism Involved in Coordinating Tissue Growth in Drosophila

A study in the Drosophila wing suggests a crucial role of p53 in the coordination of growth between adjacent cell populations to maintain organ proportions and shape

MicroRNA-Mediated Regulation of Dp53 in the Drosophila Fat Body Contributes to Metabolic Adaptation to Nutrient Deprivation

Multiple conserved mechanisms sense nutritional conditions and coordinate metabolic changes in the whole organism. We unravel a role for the Drosophila homolog of p53 (Dp53) in the fat body (FB; a functional analog of vertebrate adipose and hepatic tissues) in starvation adaptation. Under nutrient deprivation, FB-specific depletion of Dp53 accelerates consumption of major energy stores and reduces survival rates of adult flies. We show that Dp53 is regulated by the microRNA (miRNA) machinery and miR-305 in a nutrition-dependent manner. In well-fed animals, TOR signaling contributes to miR-305-mediated inhibition of Dp53. Nutrient deprivation reduces the levels of miRNA machinery components and leads to Dp53 derepression. Our results uncover an organism-wide role for Dp53 in nutrient sensing and metabolic adaptation and open up avenues toward understanding the molecular mechanisms underlying p53 activation under nutrient deprivation

Regulation and function of p53: A perspective from Drosophila studies

Tp53 is a central regulator of cellular responses to stress and one of the most frequently mutated genes in human cancers. P53 is activated by a myriad of stress signals and drives specific cellular responses depending on stress nature, cell type and cellular context. Additionally to its classical functions in regulating cell cycle arrest, apoptosis and senescence, newly described non-canonical functions of p53 are increasingly coming under the spotlight as important functions not only for its role as a tumour suppressor but also for its non-cancer associated activities. Drosophila melanogaster is a valuable model to study multiple aspects of normal animal physiology, stress response and disease. In this review, we discuss the contribution of Drosophila studies to the current knowledge on p53 and highlight recent evidences pointing to p53 novel roles in promoting tissue homeostasis and metabolic adaptation.Fil: Ingaramo, María Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Sánchez, Juan Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Dekanty, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas; Argentin